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🌿 Advantages and Disadvantages of Sexual and Asexual Reproduction

Spec 4.6.1.3 📗 Foundation
📖 In-Depth Theory

Sexual Reproduction

SEXUAL REPRODUCTION involves the fusion of two gametes (one from each parent) — fertilisation.
ADVANTAGES:
Produces GENETIC VARIATION in offspring — each individual is genetically unique.
Variation means populations can ADAPT to changing environments.
Variation reduces the risk of entire population being wiped out by a single disease (genetically diverse population = harder to infect all).
Drives EVOLUTION through natural selection acting on variation.
DISADVANTAGES:
Requires FINDING A MATE — costly in time and energy.
ONLY HALF the parent's genes are passed to each offspring (other half from mate).
SLOWER reproduction — fewer offspring produced per time period.
Some offspring may be poorly adapted (variation includes disadvantageous combinations).

Asexual Reproduction

ASEXUAL REPRODUCTION involves only ONE parent — offspring are produced by mitosis.
All offspring are GENETICALLY IDENTICAL to the parent (clones).
ADVANTAGES:
FAST — can reproduce rapidly when conditions are favourable.
No need to FIND A MATE — energy efficient.
All offspring inherit the parent's successful adaptations exactly.
100% of parent's genes passed on.
Useful when parent is well-adapted to stable environment.
DISADVANTAGES:
NO GENETIC VARIATION — all offspring identical.
If conditions change or a new disease appears, ALL offspring equally vulnerable.
Cannot evolve rapidly through natural selection.
EXAMPLES:
Asexual: bacteria (binary fission), strawberry runners, potato tubers, Hydra budding.
Sexual: most animals, flowering plants (using seeds).
SOME ORGANISMS DO BOTH:
Fungi: reproduce asexually rapidly when conditions good; sexually when stressed → creates variation.
Some plants: strawberries use runners (asexual) AND seeds (sexual).

Comparing in Context

WHEN IS EACH ADVANTAGEOUS?
ASEXUAL IS BETTER WHEN:
Environment is STABLE and parent is well-adapted.
Needing to COLONISE an area quickly — produce many offspring fast.
Example: bacteria in an ideal growth medium reproduce asexually every 20 minutes.
SEXUAL IS BETTER WHEN:
Environment is CHANGING or UNPREDICTABLE.
A new disease threatens the population — variation means some may survive.
Long-term survival of the species matters more than rapid short-term reproduction.
MANY ORGANISMS SWITCH:
Aphids: asexual in summer (fast colonisation of plants), sexual in autumn (variation for winter survival).
Slime moulds: asexual when food plentiful, sexual when stressed.
HUMAN APPLICATIONS:
Crop plants grown by asexual reproduction (cuttings, tissue culture) — all identical, high yield.
But: genetically uniform crops more vulnerable to new diseases (Irish Potato Famine example).
⚠️ Common Mistake

Asexual reproduction does NOT mean no variation ever — mutations can still occur. It means offspring are genetically identical to the parent UNLESS mutation happens. Sexual reproduction ALWAYS produces variation because of meiosis and fertilisation combining different alleles.

📌 Key Note

Sexual: two parents, gametes, variation, slower, drives evolution. Asexual: one parent, mitosis, clones, fast, no variation. Sexual advantages: variation, adaptability. Asexual advantages: speed, energy efficient. Many organisms use both. Variation = essential for evolution and disease resistance.

🎯 Matching Activity — Sexual vs Asexual Advantages

Sort each advantage into sexual or asexual reproduction. — drag the symbols on the right to match the component names on the left.

Sexual reproduction
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Asexual reproduction
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Sexual reproduction
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Asexual reproduction
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Sexual reproduction
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Variation reduces risk of whole population being wiped out by disease
No energy wasted finding a mate — all energy goes to reproduction
Drives evolution through natural selection acting on variation
Produces genetic variation — populations can adapt to changing environments
Fast — one parent can rapidly produce many identical offspring
🔬 Triple Science Only

Comparison of advantages and disadvantages of sexual and asexual reproduction (4.6.1.3) is biology-only. Includes the evolutionary significance of variation from sexual reproduction and the speed advantages of asexual reproduction.

🎯 Test Yourself
Question 1 of 2
1. A population of bacteria reproduces asexually. A new antibiotic is introduced. What is most likely to happen?
2. Why do many plants use both sexual and asexual reproduction?
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